a. The Field of the Invention
This invention generally relates to the art of providing road surfaces or pavements provided with traffic-regulating indicia thereon (such as for example a traffic lane dividing line) designed for ensuring improved nighttime visibility at substantial distance when illuminated by the light emitted by a vehicle headlamp, that is illuminated in a direction forming a very small angle with the generally planar surface of the road, the visibility being ensured by the reflection of the light which has impinged the indicium and has been reflected back towards the vehicles's driver.
More particularly, this invention is concerned with the art of forming, generally but not exclusively on upwardly facing surface of traffic-regulating indicia formed on or secured to a roadway pavement, a reflective system or arrangement essentially consisting of a plurality of suitably spaced reflective aggregates comprising exposed convex portions projecting upwardly of said surface each aggregate being arranged and constructed so that rays impinging said exposed portions at large angles of incidence will be retro-collimated, that is reflected back along their own path of incidence towards the source of light and therefore towards the eyes of the vehicle driver.
The expression "visible at distance" will indicate, as this description proceeds and in the appended claims, the condition that a discrete area of an indicium is to be clearly seen by a vehicle driver from a distance generally comprised from 34 m to 115 m about, that is from a distance (34 m about) at which a roadway pavement is fairly illuminatd by usual automobile headlamp switched to lower beam, to a distance (115 m) at which full power automobile headlamps are capable of illuminating obstacles, road variations and traffic signs, as necessary for high speed safe driving at nighttime.
Assuming that the eyes of an automobile driver are at an average height of 1.2 m about above the road pavement, it is evident that the discrete area of the indicium of the interest is seen from a direction forming a very small angle with a general plane of the indicium that is of the refractive system associated therewith. As a matter of fact, such angle is of 2.degree. about and respectively of 1.degree.10' about and of 0.degree.40' about when the distance is of 34 m and respectively of 68 m and 115 m about. Therefore, the field of this invention considers the various phenomena and effects concerned with the visibility of a sign associated with a reflective system seen in a direction forming a small angle, in particular comprised between 2.degree. and 0.degree.4' with the general plane of the same reflective system.
b. The Prior Art
The art pertinent to this invention has been detailedly described in the Patent into which my prior application Ser. No. 428,909 now U.S. Pat. No. 3,964,821 has been matured, and which is herein incorporated by reference, and therefore further comments are unnecessary thereabout, except as hereinbelow described with relation with the new and advantageous objects of this invention.